Transmission system



May 22, 1934. E. BRUCE TRANSMISSION SYSTEM Filed June 26, 1931 E. BRUCEy A TTORNEV Patented May 22, 1934 PATENT OFFICE I, 1.959.401TRANSMISSION SYSTEM Edmond Bruce, Red Bank, N. J assignor to BellTelephone Laboratories, Incorporated, New York, N. Y., a corporation ofNew York Application June 26, 1931, Serial No. 546,933

I 12 Claims. ((1250-33) This invention relates to transmission systemsand more particularly to aerial transmission systems designed tofunction at radio frequencies.

As is well known electrical transmission systems. are usually designedso that the surge, or characteristic, impedance comprising unit linearinductance and unit linear capacitance is practically constantthroughout the system, one reason being that standing waves may beeliminated by terminating a line so designed in such characteristicimpedance. In systems having conductors of uniform diameter, the linearreactive values are usually rendered constant by positioning theconductors parallel with each other. In other systems, however, as forexample, the diamond-shaped antenna disclosed in my copendingapplication, Serial No. 513,063, filed February 3, 1931, in which theconductors are by design not parallel, this method of obtaining constantreactive values obviously cannot be employed.

Moreover, certain systems are designed to have a minimum orcomparatively low impedance for the purpose of effecting a suitableimpedance match between the system and another connected system. While asuitable low impedance may be obtained with comparative ease in theparallelconductor system, the attainment of this result in systemshaving non-parallel conductors has not been satisfactorily achieved.

It is one object of this invention to obtain a constant characteristicimpedance in a transmission system comprising non-parallel conductors.

It is another object of this invention to render the impedance of anelectrical system a minimum.

It is a further object of this invention to increase the efficiency of amulti-wave directive antenna.

According to one feature of the invention at least one of twonon-parallel conductors has a generally conical shape, the conductordiameter at any point in the system being proportional to the conductorspacing at that point.

According to another feature of the invention, the unequal spacingbetween non-parallel conductors of uniform diameter is, in a sense,compensated by substituting two or more wires in place of one or bothconductors. and spacing said wires in accordance with the conductorspacing.

The invention will be more fully understood from the followingdescription taken in connection with the drawing in which:

Fig. 1A represents a transmission system comprising two non-parallelconductors, each conductor being generally conical in shape;

Fig. 1B is an end view of the conductors shown in Fig. 1A with thesignificant dimensions indicated, these dimensions also occurring inFigs. 2A, 2B and 2C infra. Each of these figures, as

well as Fig. 3, represents, when correct dimensional relations are used,a transmission line of the invention;

Fig. 2A is a cross-sectional view of a transmission line, each conductorof which comprises two wires connected in parallel;

Fig. 2B is a cross-sectional view of a transmission line, each conductorof which comprises five wires connected in parallel;

Fig. 2C is a cross-sectional view of a concentric transmissionline; and

Fig. 3 is a directive antenna system comprising V-shaped conductors,each conductor comprising two wires connected in parallel.

Referring to Figs. 1A and 13, reference numerals 1 each designate aconical shaped conductor of a transmission line, each conductor having avariable diameter D. The two conductors 1 are separated by a variablespacing "S". A source. of energy 2 and animpedance 3.are connected toone end of the line and a terminating impedance 4 is connected to theother end of the line.

If the unit reactive values for the conductors of the system shown inFigs. 1A and 1B are large compared with the resistance .stat farads isthe reciprocal of the external loop inductance expressed in abhenrys, itcan be shown that where K is a proportionality factor.

From (2) it is clearthat any increase in C wil be accompanied by acorresponding decrease in the characteristic impedance. The capacitanceper unit length for a single wire to its return conductor is given bythe relation 2s 2s ma g 103 approximately, where S=a variablerepresenting the spacing between the centers of the conductors 1;

d=a constant and represents the diameter of an ordinary transmissionconductor;

n=a variable factor;

D=nd=a variable representing the diameter of of the conductor in thesystem shown in Figs. 1A and iB'may be written;

In Fig. 2A the numeral 5 designates the two multipled wires of atransmission line conductor and numeral 6 designates the twocorresponding wires of the return conductor. The wires are of constantdiameter d and the spacing Nd" between the wirecenters varies, N being avariable factor. The conductor spacing 8'? also varies.

The system of Fig. 2B is similar to that of Fig. 2A, numerals 5designating the five wires of a transmission conductor and numerals 6,the five wires of the associated return conductor.

For the general case of "10" wires connected in multiple, such as thetwo wires shown in Fig. 2A or the live wires shown in Fig. 2B the unitcapacity may be written: f

2s 5 (Io-l) 5 E 10 dg w m approximately, and the impedance 2S Z =277 10g10 (Ix/W (6) approximately.

-In Fig. 20, reference numeral 7 designates the inner conductor andnumeral 8 the outer conductor of a concentric transmission line. Thevariable spacing between the center of the inner conductor '7 and theinner surface of conductor 8 is denoted by the symbol S; and Drepresents the variable diameter of the inner conductor. The unit linearcapacity is given by the relation where k is a constant.

The impedance is given by the relation Z 138 log 10 It will be seen fromEquation (4) that ii the ratio 25 (rt/2m is approximately constant, "10and at being constant, the impedance throughout the transmission systemsillustrated in Figs. 2A and 23 will remain constant. From Equation (8)if is constant the characteristic impedance of the system shown in Fig.20 will remain constant. Consequently, by properly choosing the spacingcharacteristic impedance is obtained in the lion'- parallel conductorsystems illustrated.

In addition to the above the characteristic impedance of a non-parallelconductor system embodying the invention is considerably lower, in acomparative sense, than the same system not modified in accordance withthe invention. Thus, if the diameter "D" of a single-wire conductor in atransmission system not designed in. accordance with the inventionequals .2 cms. and the spacing "S" between the conductors equals 1000cms., the impedance equals from Equation (4) 1100 ohms. If two wires,having a spacing such that N equals 500, or if a conical-shapedconductor having a diameter D equal to 500 d, be employed in place ofthe single-wire conductor, the impedance will equal 360 ohms, assumingthe conductor spacing S is the same in all three cases and that thediameter "12 of each wire remains constant.

It should be noted in this connection that, for a given result, the useof multiple wires in place of a solid conical conductor is morepractical and economical. Thus, equating the corresponding terms ofEquations (3) and (5). we find that the single-wiresystem illustrated inFigs. 1A and 1B and the multiple-wire systems in Figs. 2A and 23 willhave equal capacities when 2N =n For the systemof Fig. 2A the factor 11"equals 4 Ii N=500, the two-wire system of Fig. 2A'is as effective inincreasing the capacity as one wire whose diameter has been increased31.6 times. The ratio of weights of copper in the two cases is 500:1.Hence, considerable economy may be effected by employing themultiple-wire system in place of the single-wire system.

Referring to Fig. 3, a unilateral receiving antenna is illustrated.Reference numeral 9 designates a horizontal diamondshaped receivingantenna having end vertices A and B and side vertices C and D. Thisantenna comprises two V-shaped conductors oppositely positioned withrespect to each other and is similar to the antenna described in mycopending application, Serial No. 513,063, filed February 3, 1931.Reference numeral 10 designates a similar diamondshapedantennapositioned immediately below antenna 9. The correspondingsuperimposed V-shaped conductors of the two antennas are electricallyjoined at vertices A and B, and separated at vertices C and D by spacers11 which are constructed of insulating material and verticallypositioned. The ratio of the spacing Nd" between corresponding portionsof the two antennas to the spacing S between corresponding points on theV conductors of antenna 9, or ,-10, is equal substantiallyto a constant.Spacer 12, also constructed of insulating material, is horizontallypositioned and electrically separates the two V conductors of eachantenna at vertex A. The V,conductors of both antennas are connected atvertex B through a common terminating impedance 13. The antennas aresupported by means of guy wires 14 attached to wooden poles 15.Insulators 16 serve to insulate the antennas from the supportingstructure.

The antennas 9 and 10 are inductively connected through a couplingcircuit comprising transformer 1'7 and condensers 18 and 19 to a lowimpedance concentric type transmission line 20 which is associated witha receiver 21. The line is supported above ground by means of supandeffective conductor diameter, constancy in ports 22. At a point near thereceiver 21 both conductors of the concentric; line 20 are tapered forconvenience but the-ratio of the diameter of the inner conductor to theinner diameterof the outer conductor remains constant in accordance withthis invention. Arrow M represents the desired direction of reception.As described in my copending application mentioned above the projectionof each element on the vertical plane of the direction represented byarrow M is one-half a wave length less than the length of the element.

The operation of the receiving system is fully describedin my copendingapplication and will only be briefly outlined here. Energy is absorbedby the conductors of antennas 9 and 10 and transferred through thecoupling circuit to the concentric line and thence to the receiver 211..

Because of the position of the V-shaped conduc- The corresponding wiresof the two an tors and the value of the terminating impedance 13 maximumreception occurs in the direction tennas form a two-wire conductor andfunction in a manner explained in connection with Fig. 2A, Thecharacteristic impedance is therefore substantially constant throughout.the antenna system, and reflections are substantially eliminated at allfrequencies. 7 that if the \l-shaped conductors were single-wireconductors of uniform section instead of two-wire accordance with theinvention, therefore, greatly increases the antenna operating efliciencyat each frequency and also over a band of frequencies. Moreover, theantenna impedance of the system shown in Fig. 3 is considerably lessthan the impedance of either antenna 9 or 10 taken alone, and a moreeflicient transfer of energy between two antennas and the transmissionline 20 is obtained inasmuch as the line 20 has a very low impedance.Instead of the multiple-wire conductors shown, generally conicalconductors could be used, as in accordance with Fig. 1A, with likeeffect.

Although the invention has been described in connection with certaintypes of transmission systems, it is understood that it is not to belimited to any particular transmission system including transmitting andreceiving antennas. Moreover, it is obvious that conductors of otherthan circular cross-section may be employed successfully in practicingthe invention.

What is claimed is:

1. A transmission system comprising two conductors between which thespacing varies, at least one conductor having a varying effective unitcapacity area, the ratio of the effective unit capacity area of aportion of the last mentioned conductor to the spacing between saidportion and the other conductor being substantially equal to thecorresponding ratio at another portion in said system, and means forenergizing the two conductors in opposite phase.

2. A transmission system comprising two conductors between which thespacing varies, at least one conductor having a varying effective unitcapacity area, the ratio of the efiective unit capznzity area of thelast mentioned conductor at any given point to the spacing at said pointbeing equal to a corresponding ratio at the point of minimum conductorspacing, and means for energizing the two conductors in opposite phase.

stant.

It should be noted'here:

3. A transmission system comprising a plurality-oi conductorsdifierently spaced at various points in said system, said system beingenergized, at least one conductor having a varying diameter, the ratioof the diameter of said conductor at any point thereof to the conductorspacing at said point being substantially con- 4. A transmission systemcomprising a plurality of conductors differently spaced at variouscorresponding points thereof, said conductors each having a varyingdiameter, the ratio of the.

varies uniformly, the ratio of the' wire spacing v to the conductorspacing being the same at all, f

-points,-.substantially, in saidantennaa" 6. A transmissionsystemzcomprising apluralityof non-uniformly spaced conductors atleastone of' which comprises a' plurality of elements connected in parallel,the ratio of the spacing between said elements at any point in thesystem to the spacing between said conductors at said point beingsubstantially equal to the similar ratios at other points in the system.

7. In combination, a transmission system comprising a plurality oftransmitting conductors between which the spacing varies, means forenergizing said conductors, said conductors each comprising a pluralityof wires connected in parallel, the spacing between said wires varyingin degree, and the ratio of the spacing between adjacent wires to thedistance between the geometrical centers of said conductors beingsubstantially constant.

8. In combination, a translation device, an antenna associatedtherewith, said antenna comprising V-shaped conductors oppositelypositioned with respect to each other, each conductor comprising aplurality of wires connected in parallel, the ratio of the spacingbetween said wires to the spacing between said conductors being equalsubstantially to a constant.

9. In combination, an antenna having a plurality of conductors, thespacing between which varies, at least one conductor comprising aplurality of wires connected in parallel, the spacing between said wiresat any point being proportional to the spacing between said conductorsat that point.

10. In combination, a translation device, an antenna, an impedance, saidantenna connected between said device and said impedance, said antennacomprising a diamond-shaped unit superimposed on another such suit, theratio of the spacing between corresponding portions of said units at anypoint and the spacing at that point between corresponding portions ofone unit being constant.

11. In combination, a substantially horizontal diamond-shaped antennaunit each element of which is one-half of an operating wave lengthlonger than its projection on the path of the desired wave, a seconddiamond-shaped antenna unit having elements of similar length andpositioned closely beneath the first mentioned unit, a receiverconnected to one vertex, an impedance connected to the opposite vertex,the spacing between said antennas at the above mentioned vertices beingnegligible, said antennas being separated at the remaining vertices.

12. In combination, a substantially horizontal antenna comprising twoV-shaped conductors having their vertices oppositely positioned, eachhalf of the said conductors being equal substantially to one-half a wavelength plus its projection on the path of the received waves, each con-

